FIELD OF THE INVENTION
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This invention relates to an objective lens drive device and a disk device
equipped therewith. More specifically, the invention relates to the field of technology
where an objective lens drive device has movable unit which is supported rotatably and
slidably on a support shaft, and a disk device that is equipped with the objective lens
drive device.
BACKGROUND OF THE INVENTION
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There are disk devices that play signals recorded on an optical disk or other
disk-shaped recording medium. Such disk devices include ones on which is provided
an objective lens drive device that performs focusing adjustment and tracking
adjustment with respect to the disk-shaped recording medium by operation of a movable
unit that is supported on a support shaft so as to freely rotate about the shaft and freely
slide along the shaft.
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In an objective lens drive device, in the state in which no driving electric
current is supplied to the focusing coil for focusing adjustment or to the tracking coil for
tracking adjustment, it is necessary to hold the movable unit in a neutral position in the
focusing direction and in the tracking direction. Thus there are objective lens drive
devices that are constituted in such a way that, for example, a pair of bipolarly
magnetized magnets for focusing and a pair of magnets for tracking are arranged on a
fixed part, and four iron pieces corresponding to the magnets are attached to the
movable unit, and in this objective lens drive device, the movable unit has been kept in
the neutral position in the focusing direction and in the tracking direction by making use
of the fact that these iron pieces are attracted to the middle part of the magnets.
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But providing four iron pieces in this way presents the concern that it may
increase the number of parts and be a factor for higher cost, and that it may also be a
factor in preventing the objective lens drive device from being made smaller. There is
also the problem that because each iron piece must be attached in its position with, for
example, adhesion, the workability of doing so may become worse as the number of
parts increases.
SUMMARY OF THE INVENTION
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The objective lens drive device of this invention comprises a base on which a
support shaft is provided, that protrudes toward the optical axis direction of the
objective lens, that has at least a pair of magnet attachment parts, and on which magnets
are attached to said magnet attachment parts; a movable unit that is supported on the
support shaft rotatably about the shaft and slidably along the shaft, and holds an
objective lens, and has a focusing coil to which driving electric current is supplied
during a focusing adjustment of laser light that is shined through said objective lens
onto a disk-shaped recording medium, and a tracking coil to which driving electric
current is supplied during a tracking adjustment of the laser light; and magnetic
members that are formed in linear shape and are attached to the movable unit and which
hold the movable unit in a neutral position in the focusing direction and in the tracking
direction by virtue of the fact that they are attracted to said magnets.
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Also, a disk device of this invention comprises an objective lens drive device
that has a base on which a support shaft is provided, that protrudes toward the optical
axis direction of the objective lens, that has at least a pair of magnet attachment parts,
and on which magnets are attached to said magnet attachment parts; a movable unit that
is supported on the support shaft rotatably about the shaft and slidably along the shaft,
and holds an objective lens, and has a focusing coil to which driving electric current is
supplied during focusing adjustment of laser light that is shined through said objective
lens onto a disk-shaped recording medium and a tracking coil to which driving electric
current is supplied during tracking adjustment of the laser light; and magnetic members
that are formed in linear shape and are attached to the movable unit, and hold the
movable unit in a neutral position in the focusing direction and in the tracking direction
by virtue of the fact that they are attracted to said magnets. Therefore, in the objective
lens drive device of this invention and a disk device that is equipped therewith, the
movable unit is held in the neutral position by virtue of the fact that the magnetic
members are attracted to the magnets.
BRIEF DESCRIPTION OF THE DRAWINGS
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- Figure 1 is a schematic perspective view of a disk device of the present
invention;
- Figure 2 is a block diagrammatic view showing the composition of a disk
device of the invention;
- Figure 3 is an enlarged exploded side view of an objective lens drive device of
the present invention;
- Figure 4 is an enlarged top view of an objective lens drive device of the present
invention;
- Figure 5 is enlarged perspective view of a base of the drive device of Figure 3;
- Figure 6 is an enlarged top view of the first member of the drive device of
Figure 3;
- Figure 7 is an enlarged bottom view of the first member of Figure 6;
- Figure 8 is an enlarged top view of the second member of the drive device of
Figure 3;
- Figure 9 is a side view showing the first member and the second member
separated;
- Figure 10 is a front view showing the first member and the second member
separated;
- Figure 11 is an enlarged top view showing the state in which the first member
and the second member are joined together;
- Figure 12 is an enlarged side view showing the state in which the first member
and the second member are joined together;
- Figure 13 is an enlarged front view showing the state in which the first member
and the second member are joined together;
- Figure 14 is an enlarged top view of the movable unit of the drive device of
Figure 3;
- Figure 15 is an enlarged side view of the movable unit;
- Figure 16 is an enlarged front view of the movable unit;
- Figure 17 is an exploded perspective view of two magnetic members of the
drive unit of the present invention;
- Figure 18 is an enlarged bottom view of the movable unit;
- Figure 19 is an enlarged side view showing the state in which the movable unit
is supported on the base, partly in cross-section;
- Figure 20 is an enlarged top view showing the objective lens drive device with
the cover body attached;
- Figure 21 is an enlarged side view showing the objective lens drive device with
the cover body attached;
- Figure 22 is an enlarged cross-sectional view along line XXII-XXII in Figure
20;
- Figures 23, 24, and 25 are enlarged cross-sectional views and together show the
operation of the movable unit in the focusing direction, of which Figure 23 is a
cross-sectional view showing the state in which the movable unit is held in a neutral
position, Figure 24 is a cross-sectional view showing the state in which the movable
unit is moved toward the direction of arrow F1, and Figure 25 is a cross-sectional view
showing the state in which the movable unit is moved toward the direction of arrow F2;
- Figures 26, 27, and 28 are enlarged views which together show the operation of
the movable unit in the tracking direction; of which Figure 26 is an enlarged top view
showing the state in which the movable unit is held in the neutral position, Figure 27 is
an enlarged top view showing the state in which the movable unit is moved toward the
direction of arrow T1 and Figure 28 is an enlarged top view showing the state in which
the movable unit is moved toward the direction of arrow T2;
- Figure 29 is a graph showing the force Fz toward the focusing direction that
arises in the magnetic members when the movable unit is moved toward the focusing
direction;
- Figure 30 is a graph showing the rotational torque Tz toward the tracking
direction that arises in the magnetic members when the movable unit is moved toward
the tracking direction;
- Figure 31 is a diagram showing the state in which the movable unit is tilted
with respect to the support shaft;
- Figure 32 is a graph showing the rotational torque that arises in each part of the
magnetic members if the movable unit is held in the neutral position;
- Figure 33 is a graph showing the rotational torque that arises in the magnetic
members when the movable unit is in each position in the focusing direction; and
- Figure 34 is a table showing the properties of the materials used for the first
member or the second member.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
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With reference to the drawings an embodiment of the invention will be
described. The disk device (disk drive) of this embodiment is a device for playing
(reading) signals recorded on an optical disk or other disk-shaped recording medium
and/or recording (writing) signals onto a disk-shaped recording medium. The
disk-shaped recording medium is, for example a CD (compact disk), CD-ROM (CD -
read-only memory), CD-R (CD-recordable), CD-RW (CD-rewritable), DVD (digital
versatile (or video) disk), DVD-ROM, DVD-RAM (DVD - random access memory),
etc..
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As shown in Figure 1, a disk device 1 is constituted in such a way that the
prescribed members are arranged inside an outer housing 2. Arranged inside the outer
housing 2 is a chassis 3, and an arrangement hole 3a is formed in the prescribed position
in chassis 3. Below chassis 3 is arranged a drive motor 4, and a disk table 5 is fixed to
the motor shaft of drive motor 4. Disk table 5 protrudes through arrangement hole 3a
to above chassis 3.
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A lead screw 6 and a guide shaft 7 are arranged in parallel on the underside of
chassis 3. An optical pickup 8 is arranged in a position corresponding to arrangement
hole 3a of chassis 3. This optical pickup 8 is supported so as to be able to move along
the radial direction of a disk-shaped recording medium 100 mounted on disk table 5.
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Optical pickup 8 is constituted in such a way that prescribed members are
arranged on a moving base 9. One end of the moving base 9 makes a threaded
engagement with a lead screw 6, and its other end is supported slidably on a guide shaft
7. Rotation of lead screw 6 causes the moving base 9 to move toward the radial
direction of the disk-shaped recording medium 100 while being guided by guide shaft 7.
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As shown in Figure 2, an optical block 10 is arranged on moving base 9. The
optical block 10 consists of a semiconductor laser 11, a grating 12, a beam splitter 13, a
cylindrical lens 14, a photosensor 15, etc. A beam splitter 13 has a reflecting surface
13a.
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As shown in Figure 1, an objective lens drive device 16 is arranged on the
moving base 9. As shown in Figures 3 and 4, an objective lens drive device 16 is
constituted in such a way that moving unit 18 is supported on base 17.
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As shown in Figure 5, a base 17 has a base part 19, two outer yoke parts 20,
formed each bent upwards from the two side edges of the base part 19, two inner yoke
parts 21, positioned facing the outer yoke parts 20, and a baseplate attachment part 22
formed bent upwards from the rear edge of the base part 19; these parts are formed
integrally without one another. An upwardly protruding support shaft 23 is provided
approximately in the center of base part 19. A baseplate insertion hole 24 is formed
extending from the rear end of base part 19 to the baseplate attachment part 22. Outer
yoke parts 20, also operate as magnet attachment parts, and two magnets 25, each being
single-pole magnetized, are affixed respectively to their inner surfaces. Magnets 25,
for example, are each made to be an S pole. Also, magnets 25, are arranged so as to be
mutually symmetrical with respect to the centerline of support shaft 23.
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As shown in Figure 3, the movable unit 18 is constituted in such a way that a
first member 26 and a second member 27 thereof are joined together.
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As shown in Figures 6, 7, 9, and 10, the first member 26 has a joining part 28
and a holder part 29, which protrudes from joining part 28. Joining part 28 and holder
part 29 are formed integrally, for example, from liquid crystal polymer resin containing
carbon fiber. As carbon fiber-containing liquid crystal polymer resin, one may use, for
example, Vectra B230 (brand name of PolyPlastic Co., Ltd. in Japan).
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Joining part 28 has a frame part 30, which is formed roughly in the shape of a
squared-off cylinder, and a supported cylinder part 31, which is positioned roughly in
the middle of the frame part 30 and has a cylindrical shape. Supported cylinder part 31
is coupled to frame part 30 by multiple coupling parts 32. Frame part 30 consists of a
front wall part 30a, side wall parts 30b, 30b, and a rear wall part 30c. Front wall part
30a is thinner in the up-down direction than side wall parts 30b, 30b and rear wall part
30c, and its left and right side edges are connected to the lower end part of the front
edge part of side wall parts 30b, 30b. Supported cylinder part 31 is formed long in the
axial direction and protrudes above and below the frame part 30. As shown in Figure
6, provided on the upper edge of rear wall part 30c of frame part 30 are two pressing
pieces 30d, which are separated from each other and protrude toward the front. As
shown in Figure 7, provided on the lower edge of front wall part 30a of frame part 30
are two pressing pieces 30e, which are separated from each other and protrude toward
the rear.
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As shown in Figures 6, 9, and 10, provided on the upper surface of holder part
29 are positioning pieces 29a, 29a, 29a, which are separated from each other along the
circumference and form circular arc shapes. As shown in Figures 6 and 7, a
through-hole 29b is formed in the part that is surrounded by positioning pieces 29a, 29a,
29a. An objective lens 33 is positioned on holder part 29 by positioning pieces 29a,
29a, 29a and is held in place by, for example, adhesion.
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As shown in Figures 8 through 10, the second member 27 has a coil bobbin
part 34 and a protruding part 35, which protrudes rearwards from the upper edge of coil
bobbin part 34. The parts of second member 27 are formed integrally with one another
with, for example, a resin that contains glass fiber and has no conductivity. As this
glass-fiber-containing resin, one may use, for example, Zaider RC-210 (brand name of
Nippon Oil Co., Ltd. in Japan), or Sumika Super E5008, Sumika Super E5008L,
Sumika Super E5006L, or Sumika Super E5002L (brand names of Sumitomo Chemical
Co., Ltd. in Japan).
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Coil bobbin part 34 consists of a frame shaped part 36, which has a roughly
squared-off cylinder shape, and multiple coil wind-around parts 37 provided on the
outer surface of the frame shape part 36. Frame shape part 36 consists of a front wall
part 36a, two side wall parts 36b, and a rear wall part 36c. Four coil wind-around parts
37 are provided, each on a side surface of the frame shaped part 36, separated up, down,
front, and rear. Formed in the middle of side wall parts 36b, 36b of frame shaped part
36 in the front-rear direction on the upper edge and lower edge, are, respectively, two
pairs of support slits 36d, 36d and 36e, 36e.
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Provided on the rear surface of protruding part 35, and separated from each
other are four rearward-protruding end wind-around parts (end attachment parts) 35a,
35a, 35b, 35b. As shown in Figures 3 and 4, the two end wind-around parts 35a, 35a
positioned on the left side are for the focusing coil, and are attached by end parts 38a,
38b of a coil wire 38' for a focusing coil 38 being wound around them, respectively.
The other two end wind-around parts 35b, 35b positioned on the right side are for a
tracking coil, and are attached by end parts 39a, 39b of a coil wire 39' for a tracking coil
39 being wound around them, respectively. End wind-around parts 35a, 35b extending
toward the center are positioned a little below the end wind-around parts 35a, 35b that
are positioned on either side of them.
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As shown in Figures 11 through 13, first member 26 and second member 27 are
joined together by, for example, being glued together using a thermosetting adhesive.
In the state in which the first member 26 and second member 27 are joined together, the
frame part 30 of first member 26 is positioned in a state in which it is fitted into the
frame shape part 36 of second member 27. Therefore, the holder part 29 of first
member 26 protrudes forward from second member 27, and the protruding part 35 of
second member 27 protrudes rearward from first member 26.
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As shown in Figures 14 and 15, an end part 35a of coil wire 38' is wound
around one end wind-around part 35a, then it is wound around the middle part of frame
shape part 36 in the up-down direction and the focusing coil 38 is formed, and finally its
end part 38b is wound around the other end wind-around part 35a. With regard to coil
wire 39', its end part 39a is wound around one end wind-around part 35b, then it is
wound around so as to bridge a pair of coil wind-around parts 37. The winding of coil
wire 39' around the pair of coil wind-around parts 37, positioned above and below is
done in sequence around all four pairs of coil wind-around parts 37, and in this way four
tracking coils 39, are formed. Finally, the end part 39b is wound around the other end
wind-around part 35b.
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End wind-around parts 35a, 35a, 35b, 35b around which end parts 38a, 38b,
39a, 39b are wound are dipped in a solder tank filled with solder before it has hardened,
and in this way the end parts 38a, 38b, 39a, 39b are dip-soldered. As shown in Figure
4, terminals provided on one end 40a of a flexible printed circuit board 40 are connected
to corresponding dip-soldered end parts 38a, 38b, 39a, 39b.
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As shown in Figures 3, 4, 17, 18, and 19, magnetic members 41, 42 formed in
wire shape from a magnetic metal material (for example, a ferromagnetic material) are
attached to the movable unit 18. Magnetic members 41, 42 act as a spring that
generates a repelling force when elastically deformed, and they are attached to movable
unit 18 using this repelling force. Also, magnetic members 41, 42 may be formed in
the shape of a flat spring.
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As shown in Figure 17, magnetic member 41 is constituted in such a way that it
produces a base part 41a, which is long in the left-right direction, spring parts 41b, 41b,
which protrude roughly forward from both ends of the base part 41a; supported parts
41c, 41c, which protrude in mutually opposite directions from the front end of the
spring parts 41b, 41b, and magnet-facing parts 41d, 41d, which each protrude
downward from the outside end of said supported parts 41c, 41c, are formed integrally
with each other. Magnetic member 42 is constituted in such a way that base part 42a,
which is long in the left-right direction; spring parts 42b, 42b, which protrude roughly
rearward from both ends of said base part 42a; supported parts 42c, 42c, which protrude
in mutually opposite directions from the rear end of said spring parts 42b, 42b; and
magnet-facing parts 42d, 42d, which each protrude upward from the outside end of said
supported parts 42c, 42c, are formed integrally with each other.
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As shown in Figures 3 and 4, magnetic member 41 is supported by movable
unit 18 because the roughly middle part of base part 41a is pressed upward by pressing
pieces 30d, 30d of first member 26, spring parts 41b, 41b are elastically brought into
contact with the inside surface of the rear half of side wall parts 36b, of second member
27, respectively, and supported parts 41c, 41c are inserted into support slits 36d, 36d of
second member 27, respectively. Therefore magnet-facing parts 41d, are put into the
state in which they protrude from movable unit 18.
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As shown in Figure 18 and Figure 19, magnetic member 42 is supported by
movable unit 18 because the roughly middle part of base part 42a is pressed downward
by two pressing pieces 30e, of first member 26, two spring parts 42b, are elastically
brought into contact with the inside surface of the front half of two side wall parts 36b,
of second member 27, respectively, and two supported parts 42c, are inserted into two
support slits 36e, of second member 27, respectively. Therefore two magnet-facing
parts 42d, are put into the state in which they protrude from movable unit 18. These
two magnet-facing parts 42d, and two magnet-facing parts 41d, of magnetic member 41
are positioned apart from each other and one above the other.
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As stated above, two pairs of spring parts 41b and 42b, are provided on
magnetic members 41, 42, respectively, which pairs of spring parts 41b and 42b, are
elastically brought into contact with the inside surface of two side wall parts 36b.
Because of this, positioning of magnetic members 41, 42 with respect to movable unit
18 can be done very easily, and therefore the two pairs of magnet-facing parts 41d and
42d, are properly positioned with respect to movable unit 18.
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In attaching magnetic members 41, 42 to movable unit 18, it suffices if the base
part 41a or the base part 42a engages with pressing parts 30d, 30d or pressing parts 30e,
30e, spring parts 41b, 41b or spring parts 42b, 42b are elastically brought into contact
with the inside surface of side wall parts 36b, 36b, and supported parts 41c, 41c or
supported parts 42c, 42c are inserted into support slits 36d, 36d or support slits 36e, 36e.
Because of this, attachment of magnetic members 41 and 42 to movable unit 18 can be
done very easily. Also, in order to ensure the reliable attachment of magnetic members
41, 42 to movable unit 18, as stated above, in the state in which magnetic members 41,
42 are attached to movable unit 18, it suffices to fix magnetic members 41, 42 to
movable unit 18 by adhesion.
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As shown in Figure 4, by support shaft 23 of base 17 being inserted into
supported cylinder part 31, the movable unit 18 is supported on support shaft 23,
slidably along the shaft and rotatably about the shaft. The axial direction of support
shaft 23 is the focusing direction along which focusing adjustment is done with respect
to disk-shaped recording medium 100, and the rotational direction of support shaft 23 is
the tracking direction along which tracking adjustment is done with respect to
disk-shaped recording medium 100.
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As shown in Figures 3 and 4, in the state in which the movable unit 18 is
supported by support shaft 23, two magnets 25, are positioned opposite and directly
outside the magnet-facing parts 41d, 41d, 42d, 42d respectively of magnetic members
41, 42, and two inner yoke parts 21, of base 17 are positioned directly inside respective
of side wall parts 30b, of frame part 30 of first member 26.
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As shown in Figure 4 terminals provided on one end 40a of flexible printed
circuit board 40 are connected to terminal parts 38a, 38b, 39a, 39b of coil wire 38' or
coil wire 39', and the other end 40b of the flexible print circuit board 40 is glued to the
outside surface of baseplate attachment part 22 of base 17. Terminals that are
connected to a power source, which is not shown, are provided on the end 40b, and
electricity is supplied to focusing coil 38 or tracking coil 39 via these terminals.
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As shown in Figures 20 through 22, cover 43 is attached to base 17 so as to
cover the movable unit 18. Cover 43 has a top plate part 43a in which a thru-hole 43b
is formed. As shown in Figure 20, thru-hole 43b is positioned above the objective lens
33 of movable unit 18, which is supported on support shaft 23, and it is made part of the
path of the laser light that shines onto disk-shaped recording medium 100 through the
objective lens 33.
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The operation of the disk device 1 is as described as follows.
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As shown in Figure 1, when disk-shaped recording medium 100 is mounted on
the disk table 5 and the play switch (not shown), is operated, the drive motor 4 is driven,
and disk-shaped recording medium 100 on disk table 5 is rotated. As shown in Figure
2, when disk-shaped recording medium 100 is rotated, laser light is emitted from
semiconductor laser 11. This laser light is divided by a grating 12 into three types of
diffracted light -- 0-order light, +1-order light, and -1-order light -- and is shined
through the beam splitter 13 and the objective lens 33 onto the signal recording surface
(recording layer) of disk-shaped recording medium 100.
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The laser light that is emitted onto the signal recording surface of disk-shaped
recording medium 100 is reflected by said signal recording surface and is transmitted
into beam splitter 13 as returned laser light. This returned laser light is further
reflected by reflecting surface 13a of beam splitter 13 and is transmitted into cylindrical
lens 14. Astigmatism is generated by the cylindrical lens 14, then the returned laser
light travels into photosensor 15. The incident laser light undergoes optical-electric
conversion in a photosensor 15, and the electrical signal that is obtained as a result is
transmitted to RF (radio frequency) amplifier 44. An RF signal is generated in RF
amplifier 44, and a focusing error signal and tracking error signal are generated. The
RF signal is input into a signal processing circuit, which is not shown, and the focusing
error signal and tracking error signal are input into a servo circuit 45.
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Based on the focusing error signal from RF amplifier 44, the servo circuit 45
generates a focusing signal such that the value of said focusing error signal becomes "0".
Based on this focusing servo signal, current is supplied to focusing coil 38, and focusing
adjustment is done by the objective lens drive device 16 (see Figure 1). Also, based on
the tracking error signal from RF amplifier 44, servo circuit 45 generates a tracking
signal such that the value of the said tracking error signal becomes "0". Based on this
tracking servo signal, current is supplied to tracking coil 39, and tracking adjustment is
executed by objective lens drive device 16.
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As shown in Figures 2 and 19, during the focusing adjustment, movable unit 18
is operated in the axial direction of support shaft 23 in such a way that the spot of laser
light traveling through objective lens 33 is focused onto the signal recording surface of
disk-shaped recording medium 100. During tracking adjustment, movable unit 18 is
operated in the rotational direction of support shaft 23 in such a way that the spot of
laser light traveled through objective lens 33 is focused onto the prescribed position on
the signal recording surface of the disk-shaped recording medium 100.
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With reference to Figures 23 through 25, the operation of movable unit 18 in
the focusing direction is as follows.
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Figure 23 shows the state in which movable unit 18 is held in neutral position.
At this time, movable unit 18 is held in neutral position in the focusing direction
because magnet-facing parts 41d, 41d, 42d, 42d of magnetic members 41, 42 are
attracted toward magnets 25, 25, and the ends of magnet-facing parts 41d, 41d, 42d, 42d
are positioned in the middle of the magnetic flux.
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Figure 24 shows the state in which focusing adjustment is executed and
movable unit 18 is moved toward the direction of arrow F1. When current of the
orientation to move the movable unit 18 towards the direction of arrow F1 is supplied to
focusing coil 38, the movable unit 18 is moved from the neutral position in the direction
of arrow F1. At this time, a force is produced and movable unit 18 in the direction of
arrow F2 that causes magnet-facing parts 41d, 41d, 42d, 42d to be attracted to the center
of the magnetic flux generated from two magnets 25, so that if the supply of current to
focusing coil 38 (current for causing the movable unit 18 to move in the direction of
arrow F2) is stopped, the movable unit 18 once again returns to the neutral position.
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Figure 25 shows the state in which focusing adjustment is executed and
movable unit 18 is moved in the direction of arrow F2. When an electric current of an
orientation by which the movable unit 18 moves towards the direction of arrow F2 is
supplied to forming coil 38, movable unit 18 is moved from the neutral position in the
direction of arrow F2. At this time, a force is produced in movable unit 18 towards the
direction of arrow F2 that causes magnet-facing parts 41d, 41d, 42d, 42d to be attracted
to the center of the magnetic flux generated from two magnets 25, so that if the supply
of current to focusing coil 38 (current for causing movable unit 18 to move toward the
F2 direction) is stopped, the movable unit 18 once again returns to the neutral position.
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With reference to Figures 26 through 28, the operation of movable unit 18 in
the tracking direction is as follows.
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Figure 26 shows the state in which movable unit 18 is held in neutral position.
At this time, movable unit 18 is held in neutral position in the tracking direction by
virtue of the fact that magnet-facing parts 41d, 41d, 42d, 42d of magnetic members 41,
42 are attracted toward two magnets 25, and the ends of magnet-facing parts 41d, 41d,
42d, 42d are positioned in the middle of the magnetic flux.
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Figure 27 shows the state in which tracking adjustment is executed and
movable unit 18 is moved (rotated) in the direction of arrow T1. When current of the
orientation by which the movable unit 18 moves towards the direction of arrow T1,
supplied to each tracking coil 39, the movable unit 18 is moved from the neutral
position toward the T1 direction. At this time, a force is generated in movable unit 18
toward the T2 direction that causes magnet-facing parts 41d, 41d, 42d, 42d to be
attracted to the center of the magnetic flux generated from two magnets 25, so that if the
supply of current to tracking coil 39 (current for causing movable unit 18 to move
towards the T1 direction) is stopped, the movable unit 18 once again returns to the
neutral position.
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Figure 28 shows the state in which tracking adjustment is executed and
movable unit 18 is moved towards the T2 direction. When current of the orientation
by which movable unit 18 moves in the direction of arrow T2 is supplied to each
tracking coil 39, movable unit 18 is moved from the neutral position toward the T2
direction. At this time, a force arises in movable unit 18 toward the T1 direction that
causes magnet-facing parts 41d, 41d, 42d, 42d to be attracted to the center of the
magnetic flux that is generated from magnets 25, 25, so that if the supply of current to
tracking coil 39 (current for causing movable unit 18 to move towards the T2 direction)
is stopped, movable unit 18 once again returns to the neutral position.
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Figure 29 is a graph showing the force F2 that is generated in magnetic
members 41,42 when movable unit 18 is moved towards the focusing direction, because
the magnet-facing parts 41d, 41d, 42d, 42d are attracted to the center of the magnetic
flux that is produced from magnets 25, 25.
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In this graph, the vertical axis is for the force F2 that is generated in magnetic
members 41, 42; the side above the origin represents force in the F1 (+) direction shown
in Figures 23 through 25, and the side below the origin represents force in the F2 (-)
direction shown in Figures 23 through 25. The horizontal axis is for the position of
movable unit 18 in the focusing direction; the side to the left of the origin represents the
position in the F2 (-) direction taking the neutral position as the standard, and the side to
the right of the origin represents the position in the F1 (+) direction taking the neutral
position as the standard. The "Focus drive range" in the diagram indicates the range
through which movable unit 18 normally is moved in the focusing direction.
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Also, in the graph, the plot indicated by the circles "○" is data in the state in
which movable unit 18 is in neutral position in the tracking direction, and the plot
indicated by the triangles "?" is data in the state in which movable unit 18 is positioned
rotated 5.66° (degrees) from the neutral position in the tracking direction.
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As shown in Figure 29, in objective lens drive device 16, if movable unit 18 is
moved from neutral position in the focusing direction, a force to move toward neutral
position is produced in movable unit 18, so that when no focusing adjustment is done,
movable unit 18 is held in the neutral position in the focusing direction.
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Figure 30 is a graph showing the rotational torque T2 that arises in magnetic
members 41,42 when movable unit 18 is rotated towards the tracking direction, by
attraction of facing parts 41d, 41d, 42d, 42d, to the center of the magnetic flux that is
generated from two magnets 25.
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In this graph, the vertical axis is for the rotational torque Tz that arises in
magnetic members 41, 42; the side above the origin represents rotational torque in the
T1 (-) direction shown in Figures 26 through 28, and the side below the origin
represents rotational torque in the T2 (+) direction shown in Figures 26 through 28.
The horizontal axis is for the position of movable unit 18 in the focusing direction; the
side to the left of the origin represents the position in the F2 (-) direction taking the
neutral position as the standard, and the side to the right of the origin represents the
position in the F1 (+) direction taking the neutral position as the standard. The "Focus
drive range" in the diagram indicates the range through which movable unit 18 normally
is moved in the focusing direction.
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Also, in the graph, the plot indicated by the circles "○" is data in the state in
which movable unit 18 is positioned rotated 7.69° (degrees) from neutral position in the
tracking direction (the T2 direction), the plot indicated by the triangles "Δ" is data in
the state in which movable unit 18 is positioned rotated 5.66° (degrees) from neutral
position in the tracking direction (the T2 direction), and the plot indicated by the
squares "□" is data in the state in which movable unit 18 is in the neutral position in the
tracking direction.
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As shown in this Figure 30, in objective lens drive device 16, if the movable
unit 18 is moved from the neutral position in the tracking direction, a rotational force to
move toward neutral position arises in said movable unit 18, so when no tracking
adjustment is done, the movable unit 18 is held in the neutral position in the tracking
direction.
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In objective lens drive device 16, by the positional relationship between the
parts of magnetic members 41, 42 and magnets 25, 25, it is achieved that movable unit
18 is subject at all times to a rotational torque in an orientation that tilts with respect to
support shaft 23 in the R1 direction shown in Figure 31. That is, a torque that tries to
rotate movable unit 18 in the R1 direction is obtained by determining the positional
relationships such that magnet members 41, 42 are asymmetrical with respect to a
virtual plane that is perpendicular to the support shaft 23 and magnets 25, are
symmetrical with respect to the plane of symmetry. Such positional relationships are
realized by arranging magnetic members 41, 42 so as to sandwich the support shaft 23
between them in the tilt direction.
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Figure 32 shows the rotational torque in the R1 or R2 direction that is
generated in each part of magnetic members 41, 42 if the movable unit 18 is held in the
neutral position. In this graph, the vertical axis is for the rotational torque that is
produced in the R1 or R2 direction shown in Figure 31; the side above the origin
represents rotational torque in the R2 (+) direction, and the side below the origin
represents rotational torque in the R1 (-) direction. The horizontal axis is for the parts
of magnetic members 41, 42; the symbols (RA1 through RA7 and RB1 through RB7)
indicate the parts of magnetic members 41, 42 shown in Figure 17.
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As seen from Figure 32, when the rotational torque in the R1 (-) direction and
the rotational torque in the R2 (+) direction are added together, the rotational torque in
the R1 (-) direction is greater than the rotational torque in the R2 (+) direction.
Therefore it is clear that movable unit 18 held in the neutral position is subject at all
times to a rotational torque of an orientation that tilts in the R1 direction with respect to
the support shaft 23.
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Figure 33 is a graph showing the rotational torque in the R direction that is
generated in magnetic members 41, 42 when the movable unit 18 is in each position in
the focusing direction. In this graph, the vertical axis represents rotational torque in
the R (-) direction that arises in magnetic members 41, 42. The horizontal axis is for
the position of the movable unit 18 in the focusing direction; the side to the left of the
origin represents the position in the F2 (-) direction shown in Figures 23 through 25,
taking the neutral position as the standard, and the side to the right of the origin
represents the position in the F1 (+) direction shown in Figures 23 through 25, taking
the neutral position as the standard. The "Focus drive range" in the diagram indicates
the range through which movable unit 18 is normally moved in the focusing direction.
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Also, in the graph, the plot indicated by the circles "○" is data in the state in
which movable unit 18 is in neutral position in the tracking direction, and the plot
indicated by the triangles "Δ" is data in the state in which movable unit 18 is positioned
rotated 5.66° (degrees) from the neutral position in the tracking direction.
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As shown in Figure 33, it is clear that the objective lens drive device 16, the
movable unit 18 is subject at all times to rotational torque in an orientation that tilts
towards the R1 (-) direction with respect to the support shaft 23. Therefore the
movable unit 18 will be tilted in a certain direction with respect to support shaft 23, and
therefore the support shaft 23 and the movable unit 18 will make contact at points A and
B, as shown in Figure 31. In this case, center P of the load on support shaft 23 (one
point in the axial center of support shaft 23) and the drive center of movable unit 18 will
draw nearer, and thus the stable operation of movable unit 18 can be ensured at all
times.
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Also, movable unit 18 is subject to other torques, including a rotational torque
in the R direction due to its own weight and a torque in the R direction due to, for
example, flexible printed circuit board 40 being connected, but the total torque from
adding the rotational torque in the R1 direction that arises in magnetic members 41, 42
to these other torques results in a torque in the R1 direction. Therefore the movable
unit 18 is subject at all times to a rotational force in an orientation tilting toward the R1
direction with respect to support shaft 23, even in a device in which the rotational
torque due to its own weight readily varies according to the orientation when in use, in
particular in a portable disk device. Because of this, the stable operation of movable
unit 18 can be ensured.
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Also, in the objective lens drive device 16, because two magnets 25, are
single-pole magnetized, the stable operation can be obtained and the manufacturing cost
can be reduced. And because the pair of magnetic members 41, 42 is provided on the
movable unit 18, good sensitivity can be obtained, and the operation of movable unit 18
can be further optimized.
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Next, the materials used for the first member 26 or second member 27 of
movable unit 18 will be described.
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As shown in Figure 34, Vectra B230, which is the carbon fiber-containing
liquid crystal polymer resin that is used for first member 26, has high slidability, a high
flexural modulus of elasticity, and high rigidity as well. On the other hand, its surface
resistivity shows the prescribed value (that is, has conductivity), and its load deflection
temperature is low (that is, its heat resistance is low). Zaider RC-210 and Sumika
Super
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E5008, which are glass fiber-containing liquid crystal polymer resins used for
second member 27, have a lower slidability and rigidity than Vectra B230. On the
other hand, it has no conductivity, and it has greater heat resistance than Vectra 230.
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In this way, the first member 26, which holds objective lens 33 and has the
supported cylinder part 31, is formed from a material whose rigidity and slidability are
greater than those of the second member 27, while the second member 27, around which
the focusing coil 38 and tracking coil 39 are wound and which has end wind-around
parts 35a, 35a, 35b, 35b, is formed from a material that is not electrically conductive
and has greater heat resistance than first member 26. Therefore, in objective lens drive
device 16, the operation can be optimized by high rigidity and high slidability of first
member 26. In addition, because of the high heat resistance of second member 27,
dip-soldering is not impeded, and because of non-conductivity, short-circuits can be
prevented.
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By selecting the appropriate materials such as Vectra B230 to be used for first
member 26 and Zaider RC-210 or Sumika Super E5008 to be used for second member
27, a good objective lens drive device 16 can be manufactured whose operation is
highly reliable, which does not impede dip-soldering, and for which there is no danger
of short circuits.
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Also, in the objective lens drive device 16, because focusing coil 38 and each
tracking coil 39 are wound around each part of coil bobbin 34, there is no need for the
work of gluing an air-core coil onto the movable unit or the work of soldering the end of
each coil to the flexible printed circuit board, as there would be if the movable unit were
formed by gluing on an air-core coil formed by first winding a coil wire around it.
Thus the cost of manufacturing the objective lens drive device 16 can be reduced.
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Also, in the foregoing, the case was described in which movable unit 18 is
joined together with two members, first member 26 and second member 27, but the
invention is not limited to this; the movable unit may also be formed by two-color
molding. In this case, one may form, with a material that has high heat resistance or a
material that has no conduction, only the part that is prescribed for winding on a coil or
doing soldering. If the movable unit is formed by two-color molding, the
manufacturing cost can be reduced, because, for example there is no need for the work
of joining two members together.
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The specific shape and structure of each part in the above embodiment showed
in each case just an example of a realization in which this invention is implemented; the
technical scope of this invention must not be interpreted as limited to these.
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As is clear from the foregoing, the objective lens drive device of an
embodiment of this invention has a base on which a support shaft is provided, that
protrudes toward the optical axis direction of the objective lens, that has at least a pair
of magnet attachment parts, and on which magnets are attached to the magnet
attachment parts. A movable unit supported on the support shaft rotatably about the
shaft and slidably along the shaft, holds an objective lens, and has a focusing coil to
which driving electric current is supplied during focusing adjustment of laser light that
is transmitted through the objective lens onto a disk-shaped recording medium. A
tracking coil to which a driving electric current is supplied during tracking adjustment
of the laser light. Magnetic members that are formed in linear shape and are attached
to the movable unit hold the movable unit in the neutral position in the focusing
direction and in the tracking direction by virtue of the fact that they are attracted to said
magnets.
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Therefore a force is produced to move the movable unit towards the neutral
position whenever it is moved from the neutral position in the focusing direction or in
the tracking direction. That is, the movable unit is properly held in the neutral position
in the focusing direction and in the tracking direction by the minimum amount of
necessary members. And the use of linearly shaped magnetic members eliminates the
former need to have many iron pieces to hold the movable unit in the neutral position,
and reduces the manufacturing cost by reducing the number of parts and improving
work efficiency.
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Moreover, in an embodiment of the invention, provided on the magnetic
members are a pair of spring parts that are connected to the base part and both ends of
the base part and are elastically brought into contact with both side surface parts of the
movable unit. A pair of supported parts that are connected to the pair of spring parts
are supported on both side surface parts of the movable unit. A pair of magnet-facing
parts that are connected to said pair of supported parts are arranged so as to face the
magnets.
-
Thus it is very easy to position the magnetic members with respect to the
movable unit, and the magnet-facing parts can be properly positioned with respect to the
movable unit. Also, it is very easy to attach the magnetic members to the movable
unit.
-
Moreover, in an embodiment of the invention, because the magnetic members
are arranged so that the movable unit is subject at all times to rotational torque in an
orientation that tilts toward one direction with respect to the support shaft, the center of
the load on the support shaft and the drive center of the movable unit approach each
other, ensuring the stable operation of the movable unit at all times.
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Furthermore, in an embodiment of the invention, because the magnets are
single-pole magnetized, due to the simple structure, the stable operation of the objective
lens drive device can be obtained and the manufacturing cost can be reduced. In an
embodiment of the invention, because the pair of magnetic members are arranged on
opposite sides with the support shaft between them, good sensitivity can be obtained,
and the operation of the movable unit can be further optimized.
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Also, the disk device of an embodiment of this invention is a disk device in
which a disk-shaped recording medium mounted on a disk table is rotated by a drive
motor, laser light is transmitted through an objective lens held by an objective lens drive
device onto the recording surface of the rotated disk-shaped recording medium, and
information signals recorded on the disk-shaped recording medium are read and played.
The objective lens drive device has a base on which a support shaft is provided that
protrudes toward the optical axis direction of the objective lens, that has at least a pair
of magnet attachment parts, and on which magnets are attached to the magnet
attachment parts. A movable unit that is supported on the support shaft rotatably about
the shaft and slidably along the shaft, holds an objective lens, and has a focusing coil to
which a driving electric current is supplied during a focusing adjustment of laser light
that is transmitted through the objective lens onto a disk-shaped recording medium and
a tracking coil to which driving electric current is supplied during a tracking adjustment
of the laser light. Magnetic members that are formed in linear shape and are attached
to the movable unit, and hold the movable unit in neutral position in the focusing
direction and in the tracking direction by virtue of the fact that they are attracted to said
magnets.
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Therefore a force is produced to move the movable unit toward neutral position
whenever it is moved from neutral position in the focusing direction or in the tracking
direction. That is, the movable unit is properly held in the neutral position in the
focusing direction and in the tracking direction by the minimum necessary members.
And the use of linearly shaped magnetic members eliminates the former need to have
many iron pieces to hold the movable unit in neutral position, and reduces the
manufacturing cost by reducing the number of parts and improving work efficiency.
-
Moreover, in an embodiment of the invention, provided on the magnetic
members are a pair of spring parts that are connected to the base part and both ends of
said base part and are elastically brought into contact with both side surface parts of the
movable unit; a pair of supported parts that are connected to said pair of spring parts
and are supported on both side surface parts of the movable unit; and a pair of
magnet-facing parts that are connected to said pair of supported parts and face the
magnets; thus it is very easy to position the magnetic members with respect to the
movable unit, and the magnet-facing parts can be properly positioned with respect to the
movable unit. Also, it is very easy to attach the magnetic members to the movable
unit.
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Moreover, in an embodiment of the invention, because the magnetic members
are arranged so that the movable unit is subject at all times to rotational torque in an
orientation that tilts toward one direction with respect to the support shaft, the center of
the load on the support shaft and the drive center of the movable unit approach each
other, ensuring stable operation of the movable unit at all times.
-
Moreover, in an embodiment of the invention, because the magnets are
single-pole magnetized, due to the simple structure, stable operation of the objective
lens drive device can be obtained and the manufacturing cost can be reduced.
-
Moreover, in an embodiment of the invention, because the pair of magnetic
members are arranged on opposite sides with the support shaft between them, good
sensitivity can be obtained, and the operation of the movable unit can be further
optimized.